The present invention generally relates to a paper transporting device in printers, copiers and the like. More particularly, the present invention relates to a rotatable friction wheel or transporting element having friction elements, deflectable by centrifugal force, which engage the paper when driven, and which release the paper when stationary.
To increase the convenience of operation, it is known in electrophotographic printing devices operating with continuous paper to use automatic paper feeding devices. A paper feeding device of this type is described, for example, in EP-A1-0,432,298. In the known device, for the automatic threading of the continuous paper into an electrophotographic printing device through the transfer printing station and fusing station up to a delivery table, when a feeding procedure is called up, the elements of the paper transporting path and the assemblies, such as the fusing station and transfer printing station, form a paper feeding path, by means of which the continuous paper can be advanced with the aid of the tractor drive of the transfer printing station. The paper is then picked up by paper transporting rollers of a stacking device and is delivered as required. The feeding operation is controlled by an arrangement controlled by a microprocessor.
It has now been shown that simply pushing the printing medium through the paper transport channel is not sufficient, but that it is necessary to arrange additional paper transporting elements in the form of an auxiliary drive in the paper transport channel, which auxiliary drive automatically conveys the sheet fed into the paper transporting device right into the stacker. Owing to the use of heating saddles in the fusing station of such printing devices, no such paper transporting elements can be arranged below the sheet. In the case of mounting the paper transporting elements above the sheet, it must be ensured that these elements can under no circumstances touch the paper during the printing operation as otherwise the toner images, arranged loosely on the printing medium, become smudged prior to fusing.
In order to fulfil the requirements, the previously known solutions, as are described, for example, in Japan Abstract Volume 7, No. 23 (P-171) (1168) of 29 Jan. 1983, Japan Patent 57/176067, require a relatively large outlay, partly for the mechanism required for this purpose and partly for the appropriate monitoring devices.
From the literature source, IBM Technical Disclosure Bulletin, Vol. 35, No. 4B, September 1992, New York, US, pages 456-459, a device is known for aligning single sheets in a single-sheet printer. That device includes two motor-driven aligning elements which pick up the single sheets and align them on stops. For this purpose, two whips in the form of elongate rods are arranged in each case in guides of a holder, which whips are deflected due to centrifugal force during a rotary movement of the holder and thus come into contact with the single sheets. To increase the friction with the single sheets, the front ends of the whip carriers are of hollow design.
The object of the invention is therefore to provide a device for transporting printing media in printers or copiers with the aid of friction elements, in which the friction elements can be engaged with and disengaged from the printing medium in a simple manner whilst eliminating a need for pivoting devices. In particular, the device should be suitable as an auxiliary drive for an automatic printing medium feeding device in printers and copiers.